Giovanni Signorelli, INFN, Scuola Normale and Dipartimento di Fisica, Pisa PSI, February 2003 1 LXe (part B) Giovanni Signorelli Istituto Nazionale di

1Giovanni Signorelli, INFN, Scuola Normale and Dipartimento di Fisica, Pisa PSI, February 2003

LXe (part B)

Giovanni Signorelli

Istituto Nazionale di Fisica Nucleare, Dipartimento di Fisica and Scuola Normale Superiore, Pisa (Italy)

PSI, February 2003


Monte Carlo

•QE - shape

•Pile-up

•segmentation


An example of e decay


Pair events:• Signal: • Radiative decay (correlated bck)• Michel positron + -bckPositron only events:• Signal positron• Michel positronGamma only events:• Signal • with flat spectrum• Bck: from radiative decay or annihilation in flight

eγμ

Event Generation: MEGEVE


Interaction point

Energy deposit

, , z, tE

interaction in Lxe.

•Scintillation photons are traced inside the liquid Xenon and followed until they reach the PMTs

•Absorption and diffusion may occur


LiXe energy resolution

•Ineffective for short ( 1 m ) absorption length

•Important for timing resolution (see later on…)

Shape studies:Curved vs BOX (100 x 50 x 50 cm3): different geometry on position and energy resolution.

• position resolution: no difference. (10.6 mm FWHM)•a 3% systematic correction is needed on both coordinates for VLP

• energy resolution: slight improvement (from 4% to 3.5%);

• energy containment: more critical problem

a much larger volume (1.5 m3) of Xenon would be needed (and PMTs!).

QE studies:QE abs=1 m abs=

5% 6% 2.0%

10% 6% 1.7%

20% 6% 1.5%


VLP: 3.5 % Curved detector: 4 %

Energy resolution comparison•Absorption length = 1 m, various positions

•linear fit (PCA)


E/E < 4% for Abs > 1 m

(linear fit, PCA)

Energy resolution vs. absorption


Abs for last test

Observed/Expected light vs distance

Att.>1 m


Segmentation

• 6 layers of PMTs inserted at –30, 0, and 30 degrees– PMTs are placed on all walls with maximum density to keep the

homogeneity same in both segmented and non-segmented cases.

– Resolution is estimated by using simple Qsum

• We can observe more pe in case of short abs

– abs=1m: resolution 15.4%11%

• We loose efficiency due to the dead volume occupied by inserted layers of PMTs in any case.

• In case of long abs, energy leakage in the PMT layers cause deterioration of resolution in addition to the efficiency loss.

abs non-segmented segmented Eff loss(relative)

1m 15.4% 9.7% 11%

5m 3.7% 3.7% 28%

1.5% 2.0% 44%


Segmentation[2]


Reflector

• Reflector does not help to reduce the path length of scintillation light.

• Reflection efficiency (< 100%) can cause nonuniformity.

Ray=30cm

Ref eff =100%

No absoption

w/o reflector

w/ reflector


Reflector[2]


Pile-up and sensitivity

In the 90% acceptance window

Prompt background:

34 10-15per + decay

Accidental background:

2.23.5 10-14 per + decay

23107 +/sec And S.E.S. 3.65.6 10-

14

e

e+e-

Besides these high energy photons...


FULL SIM of pile up in LXeRate=23 107 /sec

Made use of no topological cut (clusters, electron, pulse shape….)

+ 5% events in the signal region

There is a 180 kHz rate of photons with E>0.5 MeV due to e

FULL SIMULATION!

How often an accidental superposition of two background events gives a signal in the 90% acceptance window around 52 MeV?

1 intrusion every 50 gates 100 ns wide

With this proportion add the signals PMT by PMT

Perform the energy reconstuction


Reconstruction of bkg events

’s from radiative decay; set of constants computed using signal events.

A small bias, but very small spill-in

of background in the signal region.


MC conclusion

• High absorption length curved shape is ok.

• QE improvement welcome (see timing resolution…)

• (accidental)2 background not harmful


MC for QE measurement?•Use the 4 alpha-sources inside the Large Prototype and compare data and MC with NO ABSORPTION ( need to use Gxe @ 170 K)

•The method depends very much on the details of the simulation (reflection on the PMT window and on walls….)

• we excluded PMTs on the alpha face but only three points left

•Need for a dedicated test station to measure all QE


PMT characterization

- FULL DESIGN AND MECHANICAL DRAWINGS COMPLETED

- CALL FOR TENDERS MADE AND JOB ASSIGNED TO THE COMPANY CINEL-Vigonza (PD), Italy

- CRYOSTAT DELIVERY EXPECTED BY THE END OF FEBRUARY

- ORDERS MADE FOR DRY UHV PUMPING GROUP, LEAK DETECTOR, UHV COMPONENTS, CRYOGENIC BOTTLE, PMT’s …

- LABORATORY PREPARATION UNDER WAY

- FOR MORE INFORMAITON ASK FRANCO


Data

•With •With runs

•With electrons

•….


LEDs-source

The LP from “inside”

-sources and LEDs used for PMT calibrations and monitoring


QE measurement•Use the 4 alpha-sources inside the Large Prototype and compare data and MC with NO ABSORPTION ( need to use Gxe @ 170 K)

•The method depends very much on the details of the simulation (reflection on the PMT window and on walls….)

• we excluded PMTs on the alpha face but only three points left

•Need for a dedicated test station to measure all QE


QE: better go 5 106

•Due to the higher Wph for Gas Xenon the alpha signal in gas used to be cut

The old quantum efficiencies were slightly over-estimated

OLD NEW


Purity and other uses

Alpha source: measured/expected light as a function of the -PMT distance

Present... Cfr. May test

Alpha source measurements: essential for purity monitor and physics measurements (n, Rayleigh,…)

Att.>1 m


Diffusion length (Rayleigh)

In Gxe consistent with Ray =

•Ratio of the charge collected on the face containing the alpha source to the total collected charge

•Independent of the absorption

Ray 70 cm

Still some systematics to be studied depending on the MC (reflections on PMT windows and LP material…)


Radioactive background w/LP

-trigger with 5106 gain

•Geometrical cuts to exclude -sources

•Energy scale: -source

•208Tl (2.59±0.06) MeV

•40K (1.42 ± 0.06) MeV

•214Bi 208Tl ??

•uniform on the front face

•few 10 min (with non-dedicated trigger)

• nice calibration for low energy ’s

40K (1.461 MeV)

208Tl (2.614 MeV)

•Seen for the first time! Studies are going on: spatial distribution of background inside the detector


Timing resolution test

t = ( z2 + sc

2)1/2 = (802 + 602)1/2 ps = 100 ps (FWHM)

Time-jitter due to photon interaction

Scintillation time, photon statistics

Measurement of sc2 electron beam

Use of Kyoto Syncrotron Ring (KSR) @ 60 MeV (2/12/026/12/02)


Timing resolution

•60 MeV e- material degradation only 128 channels (out of 228) had the TDC

•We estimate the intrinsic timing resolution vs p.e.

•divide PMTs in two groups: sc=RMS[( TL-TR)/2] at center

•TL,R = weighted average of the PMT TDCs (time-walk corrected)

0 6 12 18 24 30 36 42

Qsum (MeV)

Q/1

t

t(TDC)


TR (2)

5%10%

15%QE

•A factor of 10 in number of photo-electrons w.r.t. the Small Prototype

52.8 MeV peak

•Analysis still in progress: position-depentent corrections and cross talk problems


Resolution (preliminary)

sc = 200 ps (FWHM)Still to be done:

•event filtering

•full event reconstruction

(need to account for position correction)


V light in Xe?

•Using the correlation between the fitted coordinates of the “center” of the shower and the difference in arrival times on the various LP faces one can estimate v light and n for Xenon.

n1.7

•Need to refine the technique

•Understand via MC what is the meaning of “center of shower” and TL,R,….


Data conclusion

runs are essential for monitoring

• Xenon is pure!

• The timing resolution is consistent with the expectations but needs to be checked


Is LP completely full of LXe?1st clue: the top-source peak is higher in Lxe but not in GXe

The source somehow gets more distant from the wall! (5 mm)

MC charge collected


Lxe full? (2)

2nd clue: central spot:

a) gives a lower peak at correct z


Central Spot (2)

B) easy explanation for its position


Face Q ratio

•R-1= Charge of the face with alpha/ Charge on opposite face

•R is different for LIQUID and GAS because of Rayleigh scattering

•Rliquid 1 RGas 3


Time Evolution


Data conclusion

runs are essential for monitoring

• Xenon is pure!

• The timing resolution is consistent with the expectations but needs to be checked


End


Background distribution


Selection in z

2 is the rms of the front face charge distribution


Predicted 208Tl position

•Tl peak slightly below -peak

•Take the difference in light-yield between and (20 %)


Is the LP full of Xenon?

GXe

LXe


Clues

•Higher peak

•Position: central spot

•A low-energy peak.

•Ratio of face charges

•Develop in time


Possible Xe level

5 mm of Gxe gap


Kyoto Storage Ring

beam to LXe prototype

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Giovanni Signorelli, INFN, Scuola Normale and Dipartimento di Fisica, Pisa PSI, February 2003 1 LXe (part B) Giovanni Signorelli Istituto Nazionale di